In the case of radio systems, particularly in the case of wire-free communication systems, which allow frequency spreading by transmission of data on different frequency channels (for example frequency hopping in the case of Bluetooth), it is possible to mask out certain frequency channels in order in this way to avoid interference influences in the transmission. In the case of so-called adaptive frequency hopping methods (AFH), the frequency channels are masked out and matching to the frequency channel is carried out, automatically.
In general, a distinction is drawn between two approaches for such classification or qualification of a frequency channel, and one of these two approaches is chosen for masking out a frequency channel. In a first approach, the connection to be adapted (for example Bluetooth) is changed such that a further connection (for example WLAN=Wireless Local Area Network) is not interfered with. In the second approach, the procedure is for the connection to be adapted (for example Bluetooth) to be changed such that any possible interference from another connection has as little interference influence as possible. In this second approach, an assessment of the bit or data packet error rate on the channels is used, for example, for this purpose. In the first approach mentioned above, the field strength may be determined at times at which the connection to be adapted is not active, in order in this way to obtain information about the activity and the use of the frequency channels by another radio system.
In the second approach mentioned above it is possible, for example, to provide for the qualification of a radio channel for a bit or data packet error rate measurement always to be carried out during the reception of data or data packets. If the bit or data packet error rate measurement results in a value that is high in comparison to a comparison value, this frequency channel is subsequently inhibited or is masked out for data transmission on this frequency channel, as a result of which no more communication takes place on this frequency channel, since an interference source can be assumed, or the interference component on this frequency channel is too high.
One major disadvantage of this procedure is that it is impossible to decide with sufficient confidence the extent to which an interference source or an excessive interference component is actually present on that frequency channel. This is because it is also possible for a high bit or data packet error rate to be measured because the two communicating units in the radio system (for example two Bluetooth appliances) are a relatively long distance away from one another and, because of this fact, the received signal or data signal can no longer be sampled without errors. Thus, in this situation, an excessively high interference component would incorrectly be determined in that frequency channel, so that a frequency channel could possibly be inhibited even though no interference source or excessively high interference component is actually present. Since, in particular, this reason for an increased bit or data packet error rate is not frequency-selective, this would result in a large number of incorrect decisions being made with regard to masking out frequency channels in this situation, and would thus lead to a considerably increased number of frequencies and frequency channels which can no longer be used.
In one known channel selection method, a number of channels are provided for data transmission, via which a first and a second transmitting/receiving unit communicate without the use of wires. The digital data communication via a wire-free communication link is provided by means of data packets which are transmitted sequentially via a number of frequency channels. The communication quality of each frequency channel is recorded and is compared with a quality criterion which can be predetermined. Channels with an inadequate communication quality are replaced by previously unused channels, and/or the amount of control data which is contained in each data packet is chosen as a function of the recorded overall quality of the communication link. In the case of those methods which are used in a cordless telephone system, only a general quality figure is determined for a frequency channel, and is compared with a quality criterion. The decision as to whether a frequency channel is thus used or masked out for a data transmission can thus be made only very unreliably and inadequately. Furthermore, in this known method, a selection of one or more frequency channels is made first of all, only after which is the choice made of the data packet type with which the corresponding data will be transmitted. The quality figure for a frequency channel thus includes no information about data packet structures and data packet characteristics. The determination of an interference component in a frequency channel or whether the frequency channel is identified and classified as an interfering source can thus be made only very inadequately when using these known methods.